Having seen the debate on the economy, the only true solid ground for the Republican campaign, be systematically eroded by the extreme selection of running-mate Paul Ryan, and the sexual sideshow of Todd Akin - both manifestations of the civil war within the GOP - perhaps it was only a matter of time before the party's presumptive nominee was reduced to conspiracy theories and - let's call it what it is - old-fashioned racism.

Not that bigotry is unique to US politics. In the UK, members of the BNP and the EDL pepper their political discourse with similar innuendo. The difference is, in Britain neither of those parties are anywhere near the mainstream. Romney is running for the highest office in the land. It would be like the leader of the Tories giving a speech in which he said Keith Vaz shouldn't be trusted as "he's not from round here" or that Chuka Ummuna may have been born in London but he "isn't really one of us".

So what's particular about the US that allows this type of talk find its way into the latter stages of an election campaign?

It is less than 50 years, little more than a generation, since the passing of the Civil Rights Act in Washington, and despite steadily changing attitudes, the issue of race still pervades.

An oft-heard criticism of the 'conservative right', best known as the Tea Party since 2009, is that it is inherently racist. There has been plenty of anecdotal evidence that gives credence to this view - just look on YouTube and it's easy to find signs decrying the president as a "half-breed Muslim" or lawmakers being called "niggers" on the eve of the passing of the Healthcare Bill.

Studies on the make-up of the conservative movement, such as the 2010 paper by Professor Gary Jacobsen, argues that members of the Tea Party are more likely to harbour some form of racial resentment than non-Tea Party affiliates.

According to Jacobsen: "Tea Party activists have denied accusations that their movement is racist, and there is nothing intrinsically racist about opposing 'big government' or clean energy legislation or health care reform. But it is clear that the movement is more appealing to people who are unsympathetic to blacks and who prefer a harder line on illegal immigration..."

Though the research is far from conclusive (and was immediately attacked in the blogosphere as part of an academic liberal conspiracy to discredit the Tea Party), the notion that the 'conservative right' tends to be "older, white and male" would be difficult to argue against.

Yet racism seems to be a very specific charge to throw at such a sizable and nebulous group. A broader and more potent characteristic of the 'conservative right' appears to be the fear of change, and not just the immediate individual concerns of unemployment or higher taxes, but also the long-term remodeling of America and what it is to be an American.

In 1998, President Bill Clinton gave an address on immigration to the students of Portland State University. He said: "Today, nearly one in ten people in America was born in another country; one in five schoolchildren is from immigrant families. Today, largely because of immigration, there is no majority race in Hawaii or Houston or New York City. Within five years there will be no majority race in our largest state, California. In a little more than 50 years there will be no majority race in the United States. No other nation in history has gone through demographic change of this magnitude in so short a time. What do the changes mean? They can either strengthen and unite us, or they can weaken and divide us. We must decide."

A decade on, the US Census Bureau published a report that projected by 2042, whites would no longer be the majority of the population, though they will remain the biggest single grouping (around 70%) within the population until well after 2050.

Writing in the Atlantic in 2009, Hua Hsu argued that the rise of multi-culturalism in the US, manifested in myriad ways, from the growth of hip hop culture to Tiger Woods success on the golf course, has led to a "cultural and socioeconomic dislocation" for whites, who have become aggrieved by the sense that "the system that used to guarantee the white working class some stability has gone off-kilter."

The politics of white identity in America, or "the gradual erosion of 'whiteness' as the touchstone of what it means to be American", has left the country's white working majority adrift in a world where "'whiteness' no longer defines the mainstream."

And what greater indication of America's shifting identity than the election of a Hawaiian-born, mixed-race man with a Kenyan father and a foreign-sounding name? Not that Obama's victory triggered this crisis of identity, but in an unsophisticated way, the election of a non-white man to the presidency probably brought the issue into sharper focus for America's blue collared masses, certainly more than the projections on a Census Bureau report.

As such, those affiliated to the 'right' seem to be not only politically conservative but, in the literal sense, fearful of change. It's a fear that has revealed itself in a number of ways from the need to seek out new communities (the Tea Party as an expression of white identity) to investing in conspiracy theories that decry Obama is a secret-Muslim-fifth-columnist.

Like their John Bircher Society forebears, the Birthers, a group of people that claim that Obama is not a natural-born citizen of the United States, see only conspiracy and plot. Questions over the president's constitutional eligibility originated as a political smear, playing to base fears of 'otherness' seared into the American psyche through decades of propaganda from the Cold War to the so-called War on Terror.

The rumours started during the 2008 Democratic Party primaries, when a handful of anonymous Hillary Clinton supporters tried to reignite her faltering campaign by questioning her opponent's citizenship. Following Obama's inauguration, the rumour was picked up by the Republican blogosphere, appealing not only to those who sought to make political hay, but also the vast legions of online conspiracy theorists seeking the "truth" on everything from the 9/11 attacks to the moon landings.

Though not its defining characteristic, racism remains part of the makeup of the 'conservative right', betraying the anxieties of a social group stricken with a loss of identity and fearful of a future in which the tenets of the past have increasingly little hold.

The real tragedy for the US is that though Romney's comments may lose the candidate some votes come November, the reality is that by reducing his campaign to the level of conspiracy theory and racism, it will probably endear him to a whole lot more.